The present invention relates to a control system and a control method for a disc brake, in particular an adjuster mechanism of a disc brake.
It is known to provide an electric motor to control the running clearance of friction linings relative to a brake rotor based upon signals from sensors that monitor the clearance take-up movement and the brake actuation stroke. The known systems tend to mimic the mechanical operation of a conventional brake clearance control device, known as an “automatic adjuster.” In such adjusters, a clutch having some degree of lost motion is provided where the level of free motion is equivalent to the maximum allowable running clearance. If the friction linings wear such that the running clearance is greater than the maximum allowable running clearance, the free running clearance is “taken-up” upon operation of the brake, and the further additional free movement, caused by the excess lining clearance, causes the clutch to rotate. The rotation moves the backstop or datum position for the return of the friction lining, thus progressively advancing the friction lining towards the brake rotor as the friction lining wears. When the friction lining contacts the brake rotor, the increased load in the system causes the clutch to slip, preventing further unwanted adjustment and/or overloading of the automatic adjuster. Such mechanical automatic adjusters are well known in the art.
In the brake of the present invention, it is important to reduce weight, the power consumption (whether electrical or pneumatic) and material costs. Unfortunately, in a conventional brake having an automatic adjuster of the mechanical kind or even an electric adjuster that mimics the mechanical operation, the strength of the mechanisms of the adjuster have to be extremely high. This is because the actual brake adjustment occurs only while the brake is being applied rather than during brake release. It is common in “sliding caliper” brakes for the load to be applied directly on only one side of the brake rotor. The caliper frame slides to apply a load to the other side of the brake rotor. The load is present before both friction linings fully contact the brake rotor. Therefore, the adjuster drive train has to be capable of driving through the load.
European Patent Application 0995923 (Meritor Automotive, Inc.) teaches a pressure sensor disposed at an input end of an operating shaft (“op-shaft”) of a disc brake to determine when operation of the brake occurs and the running clearance is taken-up. The position of the op-shaft when the running clearance has been taken up is measured such that, upon brake release, the electric motor driven adjuster mechanism may move the datum position for the return of the friction lining to maintain a constant running clearance as the friction lining wears.
The present invention seeks to overcome, or at least mitigate, the problems of the prior art.